1. Technical Field
This invention relates to a process or method for controlling fossil fuel (oil or gas) furnaces under conditions of unintentional electrical power outage or situations in which there is a desire to shed electrical load such as periods of peak demand on the electric power grid.
2. Description of Related Art
Occasionally it becomes desirable or necessary to rely on backup electrical power (BUP) systems for the operation of heating, ventilation and air conditioning (HVAC) equipment. Most HVAC systems become inoperative without such backup power. Normal fossil fuel furnace control schemes are most often focused on thermal comfort rather than conservation of electrical energy. As a result such furnaces operating under normal control scenarios do not optimize electrical power usage and thereby quickly deplete BUP systems.
A few prior art references describe control schemes for emergency or backup power operation of fossil fuel furnaces. U.S. Pat. No. 4,946,096 by Ballard et al. issued on Aug. 7, 1990 (“U.S. Pat. No. '096”) discloses a control scheme for application of backup DC power to fossil fuel powered furnaces of that time period with blower and burner assemblies each having high and low settings. The control scheme restricts the furnace operation from a high heat mode during emergency power operation. As such U.S. Pat. No. '096 relies on switching to low heat mode and low circulating fan settings to reduce electrical power consumption. But, many of today's furnace designs operate more effectively, in terms of heat supplied to the conditioned space relative to the coincident electrical power usage, by remaining in a high heat mode and reducing the number of on and off cycles. As a result there remains a need to control fossil fuel powered furnaces in a manner that optimizes the heat supplied relative to the electrical energy consumed under auxiliary power conditions.
U.S. Pat. No. 5,427,086 by Brownell issued on Jun. 27, 1995 (“U.S. Pat. No. '086”) discloses a natural gas powered forced air furnace having a thermoelectric generator for providing continuous operation during an electric power outage. U.S. Pat. No. '086 applies to a self-powered system having unlimited DC power. There are no power conservation measures disclosed in the '086 patent.
Despite the use and availability of BUP systems for HVAC systems, these systems cannot be used for an unlimited amount of time. Therefore, there remains a need to optimize the manner of operation of fossil fuel powered furnaces so as to control the cycle durations in real time during periods of reduced or no electrical power so as to optimize the useful heat supplied over the limited life of BUP systems. There remains a need to improve fossil fuel powered heating systems performance when operating under DC power with limited power availability through the use of intelligent, dwelling-specific control algorithms and by providing a user interface to override such improved control algorithms when desired. The present invention fills these and other needs as detailed more fully below.